JPH071618B2 - Method of measuring the flying height of a magnetic transducer slider - Google Patents

Method of measuring the flying height of a magnetic transducer slider

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Publication number
JPH071618B2
JPH071618B2 JP62112674A JP11267487A JPH071618B2 JP H071618 B2 JPH071618 B2 JP H071618B2 JP 62112674 A JP62112674 A JP 62112674A JP 11267487 A JP11267487 A JP 11267487A JP H071618 B2 JPH071618 B2 JP H071618B2
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JP
Japan
Prior art keywords
signal
magnetic
recording medium
wavelength
slider
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
JP62112674A
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Japanese (ja)
Other versions
JPS6346617A (en
Inventor
ウオルター・ユージン・ウアシン
クラース・ベレンド・クラーセン
ジョセフ・ジャック・ラム
バイロン・リチャード・ブラウン
ヒュング・リアング・ヒュ
ヤコブス・コーネリス・レオナルダス・ヴアン・ピッペン
Original Assignee
インターナシヨナル・ビジネス・マシーンズ・コーポレーシヨン
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Priority to US06/897,180 priority Critical patent/US4777544A/en
Application filed by インターナシヨナル・ビジネス・マシーンズ・コーポレーシヨン filed Critical インターナシヨナル・ビジネス・マシーンズ・コーポレーシヨン
Publication of JPS6346617A publication Critical patent/JPS6346617A/en
Priority to US897180 priority
Publication of JPH071618B2 publication Critical patent/JPH071618B2/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/012Recording on, or reproducing or erasing from, magnetic disks
    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B27/00Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
    • G11B27/36Monitoring, i.e. supervising the progress of recording or reproducing
    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/48Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
    • G11B5/58Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B5/60Fluid-dynamic spacing of heads from record-carriers
    • G11B5/6005Specially adapted for spacing from a rotating disc using a fluid cushion
    • G11B5/6011Control of flying height
    • G11B5/6029Measurement using values derived from the data signal read from the disk
    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B2005/0002Special dispositions or recording techniques
    • G11B2005/0005Arrangements, methods or circuits
    • G11B2005/001Controlling recording characteristics of record carriers or transducing characteristics of transducers by means not being part of their structure
    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B2005/0002Special dispositions or recording techniques
    • G11B2005/0005Arrangements, methods or circuits
    • G11B2005/001Controlling recording characteristics of record carriers or transducing characteristics of transducers by means not being part of their structure
    • G11B2005/0013Controlling recording characteristics of record carriers or transducing characteristics of transducers by means not being part of their structure of transducers, e.g. linearisation, equalisation

Description

DETAILED DESCRIPTION OF THE INVENTION A. INDUSTRIAL APPLICATION Field of the Invention The present invention "flyes" over the surface of a medium when the read / write transducer is in contact with the recording medium at rest and the medium is moving at operating speed. The invention relates to a storage device of the type described above, and more particularly to a method and device for measuring the flying height of a transducer on a storage medium.

B. Prior Art High-speed data processing systems use magnetic disks to meet the requirements for large storage capacity. Data is read from and written to a disk by a magnetic converter generally called a magnetic head, and the magnetic converter is arranged on a track of the disk when data is retrieved and stored. The desire for higher data densities on magnetic disks requires that more data be read and written to the narrower tracks located on the disks. To achieve high data densities, it is necessary to narrow the transducing gap and reduce the spacing, or so-called flying height, between the magnetic transducer and the recording surface of the disk. At high data densities, it has become difficult to maintain this low flight altitude constant to the extent necessary to read and write data reliably.

Traditional methods of measuring altitude include various capacitive and optical techniques, which require special "testing".
Requires a disk or slider. These methods cannot measure the slider-disk spacing in-situ, that is, in a direct way. The actual slider-disk spacing is inferred from "test" slider or disk measurements. This method has been suitable until now, but the low flight altitude required made the accuracy of the indirect measurement method of the prior art unsatisfactory.

The effect of the head / medium spacing on the amplitude of the magnetic read signal is described by RL Wallace J.
r.) says "Reproduction of magnetically recorded signal (The Reproduc
tion of Magnetically Recorded Signals) ", Bell
System Tech Journal (Bell System Tech
nical Journal), Vol.30, October 1951, pp.1145-1173
It has been described in. This document describes Wallace's equation which represents the dependence of the read voltage on various recording parameters including the head / disk spacing.

Using the envelope of the read signal to measure head / disk spacing variations is described in IBM Technical Disclosure Bulletin, Vol. 11, No. 12, May 1969.
"Head Flight Height Monitoring" by Baudet et al., P.1650, Mon.
It is described in. The control rates described in this article are based on comparing the currently detected read signal level to an average of previously detected levels.

Modulation of the read signal envelope for measuring head / disk spacing variations is described in Shi et al., “Read signal modulation for measuring head / disk spacing variations in magnetic disk files. Use (Us
e of Readback Signal Modulation to Measure Head / Di
sk Spacing Variations in Magnetic Disk Files) ",
Technical Report No.11, The Magnetic Recording Research Center, University of California (San Digo)
Center for Magnetic Recording Research, University
of California, San Diego), December 1985. Readout signal modulation technique is used with a laser Doppler vibrometer to simultaneously measure both spacing variations and disk variations due to various shocks directly in the lab to a working disk file. . Although this device is useful as a laboratory tool in the research and development of magnetic disk files, in order to adapt it to the laser Doppler vibrometer, the structure of the disk file must be changed, Also, the equipment required is extremely expensive.

Morris et al., “IEEE Trans.on Magnetics MAG-17”, No.
4, July 1981, pp.1372-1375 article "Off-track
Effect of flight altitude variation on data processing (Effect o
f Flying Height Variation on Offtrack Data Handlin
g) ”infers flight altitude variations by modulating the magnetic head read signal and correlates flight altitude variations with off-track data processing capability.

C. PROBLEMS TO BE SOLVED BY THE INVENTION The prior art did not have a method and apparatus for directly measuring the distance between a magnetic transducer and a recording medium in-situ in a magnetic disk storage system.

D. Means for Solving the Problems Therefore, a main object of the present invention is to provide a method and apparatus for directly measuring the distance between a magnetic transducer and a recording medium in-situ in a magnetic disk storage system. Is.

In accordance with the present invention, a method and apparatus for measuring the flying height of a slider bearing a magnetic transducer in an operating magnetic storage system is provided that provides a relative motion between a magnetic conversion and a magnetic recording medium at a first velocity v. And the resulting air bearing includes positioning the magnetic transducer slider at a first flying altitude from the magnetic medium. A single signal with a constant period T is
A first signal is generated by writing to a predetermined area of the recording medium and detecting a read signal from the predetermined area of the recording medium. The flying height of the slider of the magnetic converter is reduced to almost zero,
The read signal is detected at the lowered flight altitude and the second signal is generated. Then the first flight altitude is multiplied by the wavelength w,
It is calculated as the ratio of the first signal and the second signal in decibels divided by a constant.

In another embodiment, a plurality of signals having a constant period T 1 , T 2 , ... Tn are written in a predetermined area of a recording medium, a read signal is detected at a first wavelength, and a first signal is generated. , Simultaneously detecting the read signal at the second wavelength and generating the second signal. The flight altitude is reduced to almost zero and the read signal is set to 2
Detect at one wavelength and generate a third and a fourth signal.
Next, the first flight altitude is calculated as a constant multiplied by the product of two terms. The first term is the product of the two wavelengths divided by the difference between the two wavelengths, and the second term is the ratio of the first and second signals in decibels, the third and fourth in decibels. It is subtracted from the signal ratio.

Yet another embodiment of the present invention uses at least one signal of a constant period T written in a predetermined area of a recording medium, so that a read signal has a spectral content composed of a plurality of different frequencies. Is. The read signal is detected from a predetermined area of the recording medium at the first wavelength W1 = vT, the first signal is generated, and at the same time the read signal is transmitted at the second wavelength Wn.
= NvT (a positive number of n ≠ 1), a second signal is generated by detecting from a predetermined area of the recording medium. Then, the flying height of the magnetic transducer slider is reduced to substantially zero, and the read signal is lowered to detect the flying height at two frequencies,
Generates third and fourth signals. Next, the first flight altitude is calculated as the product of two terms. The first term is a constant times the velocity v divided by the frequency difference between the first and second signals, and the second term is the first and second at two wavelengths in decibels. It is the difference between the ratio of the read signals and the ratio of the third and fourth read signals at the two wavelengths expressed in decibels.

The above and other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments of the present invention shown in the accompanying drawings.

E. Embodiments The present invention will be described as being applied to a magnetic disk storage device. However, for those skilled in the art, the present invention is not limited to this, and other mechanically moving magnetic storage devices can be used. It will be clear that it can also be applied to devices.

As shown in FIG. 1, in a conventional magnetic disk file, a plurality of rigid rotating disks such as disks 10, 12 and 14 are supported on a spindle 16 and rotated by a disk drive motor 18, The rotation speed of is detected by the sensor 20. The magnetic recording medium on each disc has an inner diameter of 22 and an outer diameter as shown on disc 10.
It is in the form of an annular concentric data track with 24.

As the disk rotates, the slider moves radially so that the head can access different portions of the disk surface containing data. Each slider 26 carries one or more read / write heads,
And the actuator arm by suspension 30
It is attached to 28. The suspension 30 provides a light spring force which biases the slider against the disk surface. Each actuator 28 is a voice coil
It is attached to the motor (VCM) 32. The VCM is a coil movable in a fixed magnetic field, and the moving direction and speed of the coil are controlled by the supplied current.

During operation of the disk file, the rotation of the disk creates an air bearing between the slider and the disk surface. This air bearing therefore balances the light spring force of the suspension and supports the slider away from the disk surface during operation.

The above description of a typical disk file, and the first
The parts of the figure related to this are for illustration purposes only. It will be appreciated that a disk file can contain multiple disks and VCMs, and each VCM can support multiple sliders. The method and apparatus of the present invention for measuring the flying height of a head on a disk surface is of the type in which the slider is in contact with the storage medium at rest and "flyes" over the storage medium at operating speed.

In operation, the various components of the disk file are controlled by signals generated by controller 34, which includes internal clock signals, logic circuits, memory and microprocessors. Controller 34 generates control signals such as motor control signals on line 36 and position control signals on line 38 to control various operations of the disk file. The control signal on line 38 provides the desired current profile to optimize the movement of the selected slider 26 to the desired track on the associated disk.

As shown in FIG. 2, sliders 26a and 26b are initially arranged such that they are on one or more tracks 42 and 44 which form a landing zone on a plurality of data tracks 46 and 48. . According to the present invention, the signal is recorded in a predetermined area on the disc, which is preferably part of tracks 42 and 44 of the landing area, but either of the data track areas 46 or 48. It doesn't matter. The pattern to be recorded is processed by the write channel 33 (FIG. 1) and coupled to the write driver forming part of the arm electronics 29. Magnetic transducer
The read signal from 27 (Fig. 3) is, first, the arm electronic circuit.
It is amplified by a preamplifier that is part of 29 and then processed by the read channel 35.

The terms flight altitude, spacing, and clearance have different etymologies and meanings, but are used interchangeably in the art to some extent. Flying height was originally used to describe the optically measured distance between the magnetic transducer slider and the recording medium, while the spacing is the magnetic distance between the magnetic transducer and the magnetic recording medium. The distances defined by the above, and these values may differ due to the presence of a protective layer on the recording medium, for example. The term gap is the physical gap between the magnetic transducer slider and the surface of the magnetic recording medium, which is what is referred to as the flying height when measured by the method of the present invention.

As shown in FIG. 3, the magnetic transducer slider 26 is spaced apart from the magnetic recording medium surface 40 by an air bearing formed by the relative motion between the slider 26 and the magnetic recording medium indicated by arrow 39. Supported. In the illustrated embodiment, the shape of slider 26 is such that the flight attitude at normal relative velocity v positions magnetic read / write transducer 27 at a distance d from recording medium surface 40.
Transducer 27 is preferably an inductive read / write head, but the invention is equally applicable to independent read and write transducers mounted on the same slicer, and induction mounted on the same slider. It is also applicable to magnetic write transducers and magnetoresistive read transducers. The read transducer and write transducer need not be mounted on the same slider, in which case it is the spacing of the read transducer that is detected.

According to the present invention, there is provided a method and apparatus for measuring the flying height of all magnetic heads of a magnetic disk storage system. Using this method is invoked by a signal generated by controller 34, FHM. According to this method, the read signal is controlled by the FHM signal from the controller 34 and is also coupled to the flight altitude measuring means 49.
The theoretical basis of this method and apparatus is the Wallace spacing loss equation, which expresses the dependence of the read voltage on various recording parameters including head / disk spacing. This equation can be expressed as:

However, λ = wavelength of the pattern recorded on the disc Eo = amplitude of a certain reading E = amplitude of the next reading For the correction coefficient, Vo = speed at the time of measuring Eo V = speed at the time of measuring E G = Frequency Response of the System The correction coefficient equation (2) above is applicable to the inductive read transducer. However, when using a magnetoresistive read transducer, the first Vo / V is replaced by 1. The above equation (1) shows that the fluctuation of the signal measured in decibel can be converted into the change of the interval or the flight altitude. Knowing the change in spacing or flight altitude provides some useful information, but what is desired is the absolute flight altitude. The absolute flight height can be measured in some way by reducing the slider clearance on the disk to a reference clearance, such as zero, so that a reference reading at a reduced clearance, such as zero clearance, can be obtained. The clearance can be reduced, for example, by applying mechanical force or by expelling gas from the air bearing. A preferred method of reducing the slider clearance on the disk, called "spin down", is to slow the disk so that the air bearings are destroyed and the slider contacts the disk. As shown in FIG. 5, as velocity decreases, so does the gap and a read signal is detected at each of the velocity points. If the corrected signal (ie, the signal corrected by equation (2)) no longer increases, this indicates that the slider has contacted the surface of the disk. Even if the slider comes into contact with the surface of the disk, a sufficient read signal is produced by the transducer 27 to produce an accurate flying height reference signal, as the velocity is still well above zero. The absolute flight altitude can then be calculated as the sum of the values from the Δ flight altitude calculated at zero spacing to the one calculated at the normal operating speed of the disk file. The absolute flight altitude can be calculated as the ratio of the signal detected at the first flight altitude to the signal detected at zero gap, expressed in decibels, multiplied by the wavelength and divided by a constant.

In order to obtain an accurate measurement of flying height, the amplitude of the read signal must be measured by the magnetic head aligned with the track on which the test signal is written. Typically, high performance magnetic disk files have a tracking servo system that operates only when the disk is spinning at normal speed. In these systems, the test signal is preferably written by an actuator located near the crash stop at the end of motion. Second
As shown, the test signal is preferably written to track 42 or 44 when actuator 28 is near crash stop 31. Then, "Spin
Because a small amount of alternating current is applied to the VCM 32 during "down," the resulting motion causes the actuator 28 to move away from the crash stop 31 and the slider dither motion 25 (FIG. 2) across the recorded track. ) Can be caused. This movement allows the peak detector 56 to capture the amplitude of the peak read signal when the magnetic transducer 27 crosses the center of the track 42 or 44 in which it is written. By de-energizing the drive motor 18, "spin down" is initiated and the sensor
The relative speed during spin down can be detected by referring to the MP (MOTOR SPEED) signal provided by 20 or by referring to the frequency of the read signal.

FIG. 4 shows a block diagram of the apparatus for a particular embodiment for carrying out the present invention. The multiplexer 50 makes it possible to detect the read signal from a particular one of all the magnetic heads, and the high-frequency amplifier 52 gives the amplified signal. The output of amplifier 52 is coupled to tracking bandpass filter 54, from which the signal is coupled to peak detector 56. The peak detector 56 detects the peak amplitude of the read signal, and this value is the analog-to-digital converter (ADC) 58.
And provides a digital representation of the peak amplitude of the read signal. The digital signal is then coupled to a processor 60, where the calculations according to equations (1) and (2) are performed. In a particular embodiment, multiplexer 50 and high frequency amplifier 52
Since it already exists in the disk file, all that is required is a logic circuit responsive to the FHM signal to gate the read signal to these components. The tracking bandpass filter 54 and the peak detector 56 are the devices that must be added to carry out this method, these components being combined in the frame of the flight altitude measuring means 49. The ADC 58 and processor 60 are already available in a disk file. A microprocessor in the controller may be used for processor 60, or a well-known model 808 from Intel Corporation of Santa Clara, California.
You can use a dedicated microprocessor such as an 8 microprocessor.

The tracking bandpass filter 54 has a dual function of a filter and a frequency tracking. The tracking bandpass filter 54 comprises a frequency mixer, a variable frequency local oscillator, a bandpass filter, and an intermediate frequency tuning amplifier. The filter function makes it possible to detect only the amplitude of the fundamental frequency of the read-out signal according to the assumption that Wallace analysis is valid. An additional function of the bandpass filter is to increase the signal to noise ratio in amplitude measurements. The frequency tracking feature allows the filter to adapt to changes in the frequency of the read signal as the speed of the disk changes. The tracking function operates in response to the MP signal derived from the sensor 20 or the frequency of the read signal.

The simplest implementation of this invention is to utilize only the recorded signal having only a single wavelength λ, which is recorded at a specific location on the disc, which location is initially Tracks 42 and 44, or one of the data tracks 46 or 48. The data already recorded on a specific track may be used. The preferred recorded tracks consist of the tracks recorded in the initial track 42 or 46, and the tracks are preferably recorded at the frequency of the clock source already available in the file. For example, a signal with a frequency of 20MHz,
Signals of shorter wavelength are preferred.

The second embodiment of the present invention utilizes a dual wavelength method for measuring head / disk spacing changes. This method has inherent long-term stability and is therefore suitable for being incorporated into a disk file to provide a warning of loss of head / disk gap that could lead to head crush. In the double wavelength method, two wavelengths λa
And λb on adjacent tracks, or on one of the tracks or track segments,
Preferably, it is necessary to either insert and record. Since the zero gap value is measured as described above, the absolute flight altitude can be measured. Then 2
By measuring only the ratio of the amplitudes of the read-out signals at one wavelength, any change in flight altitude that occurs between the first and subsequent measurements can be calculated by:

Where R 1 and R 2 are the ratios of the signal amplitudes measured for the two wavelengths at times 1 and 2. The left side of this equation is formally obtained by calculating the relative altitude, but since d1 is practically 0, the absolute flight altitude can be calculated. In other words, the absolute flight altitude is
It can be calculated as a constant multiplied by the product of two terms. Two
The first of the two terms is the product of the two wavelengths divided by the difference of the two wavelengths and the second of the two terms is the amplitude A1 of the first signal measured at time 1 above. And the ratio of the amplitude A2 of the second signal in decibels (lnA1 / A2
= LnR1) and the amplitude A3 of the third signal measured at time 2
And the fourth signal amplitude A4 ratio expressed in decibels (lnA3 / A4 = lnR2), the difference is lnR2-1nR1 = ln (R2 / R1). By using this embodiment, signal perturbations such as gain drift and track misalignment do not change the ratio of the measured signals, so long as they are independent of wavelength, and thus do not introduce errors.

FIG. 6 is a block diagram of an apparatus for implementing a dual wavelength embodiment of the present invention. This device is a multiplexer
50 and high frequency amplifier 52, which function in a similar manner to the single signal embodiment. Each wavelength λ
Two tracking bandpass filters 54a and 54b are provided, one for tracking a and λb.
Park detectors 56a and 56b detect the peak amplitude of the signal, which is the analog-to-digital converter (ADC) 58a.
And 58b are converted to digital form. Two
The transformed values of the two signals are coupled to the processor 60 and the flight altitude is calculated according to the above equation.

Another embodiment of the invention is the Harmonic Ratio Flying Height (HRF) method, which is a signal whose read spectrum is constant along the track and whose amplitude is not zero for at least two frequencies. Is based on writing. Such a pattern can be obtained by writing several passes on the same track, each with a different wavelength, these wavelengths being associated harmonically with the reduced write current and the written spectral line. May or may not affect the relative size of. The preferred write signal is a single pass write of a periodic signal (single wavelength W, constant transition density) at a write current normally used to write data.

A write signal can be selected that matches the coding and writing capabilities of the file, for example, a valid code recorded in a single repeating waveform along the entire length of a track or track segment. It is composed of concatenated words and provides a square wave write current. In this case, the read signal V (t) is a periodic signal with a fundamental frequency f 1 ′ = v / w recorded at a linear velocity v.
The spectrum of the read signal V (t) is mainly frequency fn = n ×
It consists of odd harmonic lines at f 1 ′ (n = 1, 3, 5). From this spectrum, the instantaneous amplitude V (f 1 ) of the fundamental frequency f 1 and the instantaneous amplitude V (fn) of the odd harmonics at the frequency fn are simultaneously measured. The HRF measurement method produces an instantaneous output signal Vout (t) equal to the logarithm of the ratio of the two detected amplitudes (f 1 ) and V (fn) of the two spectral lines f 1 and fn of the read signal V (t). Bring

K is a gain factor. This can be shown using the Wallace equation to be equal to

In this case, C is the gap d when writing the signal and Δf =
is independent of the constant and fn-f 1, v is the linear velocity at the time of writing.

The above measurement does not yield the absolute value of the gap d, since the measured value contains a constant of unknown value. However, if the second reference measurement is made at a known value of d (eg, d = 0), a constant can be calculated and this can be subtracted from the measured signal Vout (t). It can be assumed that the condition d = 0 exists during the low velocity at which the slider is in contact with the surface of the medium, which can be achieved by using the "spin down" approach described above.

In the absence of such a reference measurement, the measurement described above measures the change in the gap, for example from d = d 1 to d = d 1 + Δd. This causes a change in output voltage.

Where Δd is the change in gap between the two measurements.

The above equation can be solved for Δd to calculate the flight altitude. In this case, the absolute flight altitude can be calculated as the product of two terms, but the first term is a constant v
Multiplied by and divided by the difference in frequency between the first and second signals, the second term being the decibel of the first and second read signals (at the first flight altitude) at the two frequencies. The difference between the expressed ratio and the decibel ratio of the third and fourth read signals (at the reference flight altitude) at the two frequencies.

The HRF measurement method is a continuous, instantaneous measurement of the ratio of two spectral lines V (f 1 ) and V (fn) in the spectrum of the read signal V (t). Both instantaneous line amplitudes are associated with the same volume element of the recording medium beneath the head. This makes the measurements essentially insensitive to disturbances such as those caused by amplifier gain, head efficiency, effective track width, misalignment, media velocity, magnetic moment, and media thickness variations. . Furthermore, by the HRF measurement method, the instantaneous head gap Vou
Not only can t (t) be determined, but head clearance Vout
It becomes possible to properly determine the average track average value of (t).

FIG. 7 shows a particular embodiment of the apparatus used to perform the HRF method using phase sensitive detection of the two harmonics of the read spectrum. However,
The present invention is not limited to phase sensitive detection. The input signal V (t) is an analog read signal from the read preamplifier output. The harmonic line amplitudes V (f 1 ) and V (fn) at frequencies f 1 and fn are detected by two interfering (or synchronous) detectors 62 and 64. These detectors detect only the components of their respective spectral line amplitudes that are in phase with the fundamental harmonic frequency f 1 of V (t), which is the read signal V to the phase locked loop 66. This is achieved by inputting (t). The clocking output of the phase locked loop 66 at frequencies f 1 and fn is coupled to the interference detector and is
It gives an output signal equal to the instantaneous magnitude of the two selected spectral lines. A log ratio circuit 68, which includes a divider 70 and a log compressor 72, serves to determine the log of the instantaneous amplitude of a pair of spectral lines. In the preferred embodiment, only the first and third harmonic lines of the frequency spectrum are used, as these are the harmonic lines with the highest signal to noise ratio. In addition, when a switching type modulator (SD of 62 and 64) is used for the interference detectors 62 and 64, 1/8 of the output of the detector 64 is subtracted from the output of the detector 62, and V (f 1 ) is You can also get it. In this way
The harmonic sensitivity of the switching modulator SD can be compensated.

F. Effects of the Invention The invention is not limited to the first and third harmonic ratios. Using this invention, all independent ratios between harmonics can be measured and the resulting gaps averaged and weighted by the respective signal-to-noise ratio of the amplitude of each harmonic line. Can be attached.

[Brief description of drawings]

FIG. 1 is a simplified block diagram of a disk file implemented by the present invention. FIG. 2 is a diagram showing the access mechanism for the single disk surface of the apparatus of FIG. FIG. 3 is a side view showing the position of the slider between the slider and the magnetic recording medium at the normal relative speed. FIG. 4 is a block diagram of an apparatus for making flight altitude measurements according to a particular embodiment of the present invention. FIG. 5 is a graph of the relative velocity between the magnetic transducer and the disk surface against the gap between the magnetic transducer and the disk surface. FIG. 6 is a block diagram of an apparatus for performing another embodiment of flight altitude measurement. FIG. 7 is a block diagram of an apparatus for performing yet another embodiment of flight altitude measurement. 10, 12, 14 ... disk, 16 ... spindle, 18 ... disk drive motor, 20 ... sensor, 26, 26a, 26b ... slider, 27 ... magnetic transducer, 28 ... actuator arm, 29 …… Arm electronic circuit, 30 …… Suspension,
31 …… Crash stop ・ 32 …… Voice coil ・
Motor (VCM), 33 ... Write channel, 34 ... Control device, 35 ... Read channel, 40 ... Magnetic recording medium surface, 49
...... Flying altitude measuring means, 50 …… Multiplexer, 52 ……
High frequency amplifier, 54, 54a, 54b ... Tracking band filter, 56, 56a, 56b ... Peak detector, 58, 58a, 58b ...
… Analog-to-digital converter (ADC), 60… Processor, 62, 64… Interference (or synchronization) detector, 66… Phase locked loop, 68… Logarithmic ratio circuit, 70… Divider , 72
…… Logarithmic compressor.

Front Page Continuation (72) Inventor Kras Belend Klaersen 7171 Anjo Creek Circle, San Jose, Calif., United States (72) Inventor Joseph Jack Lamb, 6326 Desert Frame Drive, San Jose, Calif. Land (72) Inventor Jacobs Cornelis Leonardas Vuen Pippen 841 Portswood Circle, San Jose, Calif., United States 841 (72) Inventor Walter Eugene Huacin San Jose, Calif., USA, Coffeewood Court 769

Claims (4)

[Claims]
1. A slider is provided which causes relative motion at a predetermined speed between a magnetic transducer and a magnetic recording medium, and a slider which supports the magnetic transducer by an air bearing resulting therefrom has a flying height from the recording medium. The magnetic converter writes a signal of a predetermined cycle in a predetermined region of the recording medium, the magnetic converter detects a read signal at a predetermined wavelength from the predetermined region to generate a first signal, and the slider is substantially To generate a second signal by detecting a read signal at the predetermined wavelength from the predetermined region in a state of being in contact with the surface of the recording medium, and the predetermined ratio to the ratio of the first signal and the second signal expressed in decibels. A method of measuring the flying height of a magnetic transducer slider, comprising multiplying the wavelength and dividing by a constant to calculate the flying height.
2. A slider for providing relative motion at a predetermined speed between a magnetic transducer and a magnetic recording medium, and supporting the magnetic transducer by an air bearing which results therefrom, is arranged with a flying height from the recording medium. , T1, T in a predetermined area of the recording medium by the magnetic converter
2. Write a plurality of signals having a plurality of periods of Tn, detect a read signal at the first wavelength from the predetermined region by the magnetic converter, generate a first signal, and generate a first signal by the magnetic converter. A read signal is detected from a predetermined area at a second wavelength to generate a second signal, and the magnetic transducer is used to move the second signal from a predetermined area of the recording medium in a state where the slider is substantially in contact with the surface of the recording medium. A read signal is detected at the first wavelength and the second wavelength to generate a third signal and a fourth signal, respectively, and a product of the first wavelength and the second wavelength is a constant and the first wavelength and the second wavelength are obtained. The first term divided by the difference in wavelength, the difference between the decibel representation of the ratio of the first signal and the second signal and the decibel representation of the ratio of the third signal and the fourth signal. Calculate the flight altitude by multiplying the binomial and A method of measuring the flying height of a magnetic transducer slider, including:
3. A slider, which provides relative motion at a predetermined speed between a magnetic transducer and a magnetic recording medium, and which supports the magnetic transducer by an air bearing which results therefrom, is arranged with a flying height from the recording medium. A signal having at least one period T is written in a predetermined area of the recording medium by the magnetic converter, and a read signal at a first wavelength is detected from the predetermined area by the magnetic converter to generate a first signal. Then, the magnetic converter detects a read signal from the predetermined region at a second wavelength that is an integer multiple of the first wavelength, and generates a second signal, and the slider is substantially on the surface of the recording medium. In a contact state, the first wavelength from the predetermined region of the recording medium by the magnetic converter, the read signal is detected at the second wavelength to generate a third signal, respectively a fourth signal, A constant, a first term obtained by dividing the predetermined speed by a difference between a frequency relating to the first signal and a frequency relating to the second signal, and a decibel representation of the ratio between the first signal and the second signal. A method of measuring the flying height of a magnetic transducer slider, comprising: multiplying the second term, which is the difference between the third signal and the fourth signal expressed in decibels, to calculate the flying height. .
4. A slider that supports the magnetic converter by an air bearing generated between the magnetic converter and the magnetic recording medium when the magnetic recording medium rotates at a predetermined speed by using the Wallace space loss equation. A method of obtaining an absolute value of a flying height when flying from a position where the slider is substantially in contact with the recording medium by lowering the rotation speed of the recording medium, and a read signal in the state is obtained. Is compared as a reference value of a read signal at the flying altitude.
JP62112674A 1986-08-15 1987-05-11 Method of measuring the flying height of a magnetic transducer slider Expired - Lifetime JPH071618B2 (en)

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US06/897,180 US4777544A (en) 1986-08-15 1986-08-15 Method and apparatus for in-situ measurement of head/recording medium clearance
US897180 1992-06-11

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JPS6346617A JPS6346617A (en) 1988-02-27
JPH071618B2 true JPH071618B2 (en) 1995-01-11

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EP0256356A2 (en) 1988-02-24
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US4777544A (en) 1988-10-11
EP0256356B1 (en) 1993-09-15

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